A wide variety of fluid pressure relief apparatus have been developed and used heretofore. Such apparatus may include a rupturable member supported so that when the internal pressure of the vessel contents gets too high or exceeds a predetermined level, rupture occurs and fluid pressure is relieved. On the other hand, quite apart from internal pressure, rupture can occur through destruction of the vessel due to increasing temperature of the material of which the vessel is made.
It can be appreciated that a safety relief valve that opens at a certain pressure value gives some protection against overheating of the vessel itself. However, under certain conditions, such as a partially filled vessel or one made of a material which undergoes a relatively rapid deterioration of its tensile strength or other physical property with increasing temperature, a pressure responsive apparatus may not be sufficient to relieve the pressure before the stresses induced in the vessel exceed the predetermined level. Because of this, it is advantageous to employ a relief apparatus which has both temperature and pressure sensing mechanisms which are independent of each other.
Regarding the material of which the vessel is made, thick walled metal pressure vessels typically have a reasonably long endurance when subjected to high temperatures, such as being engulfed by flames due to a fire, and thus are often protected from catastrophic failure by a pressure type apparatus that ruptures at 25-50% above normal pressure. On the other hand, filament composite pressure vessels typically have much shorter endurance times, and generally the vessel contents do not incur a substantial pressure rise before the structure deteriorates sufficiently to cause a catastrophic failure. Thus, filament composite pressure vessels often are protected from catastrophic failure mostly by a thermally activated relief apparatus. Yet, the contents of the vessel still may require a rupturable-type pressure safety mechanism.
Heretofore, combination temperature responsive pressure relief apparatus have been fairly complicated and expensive to manufacture. This is because of the multiple components used in the apparatus. For instance, U.S. Pat. Nos. 4,352,365, to Boccardo et al, dated Oct. 5, 1982; 4,744,382, to Visnic et al, dated May 17, 1988; and 4,750,510, to Short, dated Jun. 14, 1988, are but some examples of combination temperature responsive pressure relief apparatus of the multiple-component type. In other words, each of these patents show one form or another of a plug or other component that is held in place or otherwise operatively associated with a fusible member or material. This provides the temperature responsive means for the apparatus. In addition, a completely separate pressure responsive member, such as a rupturable diaphragm, also is used to provide the pressure responsive portion of the combined apparatus. Sometimes, additional components must be required to hold the rupturable diaphragm in position. In other types of apparatus, separate components must be used to hold a fusible component in position. It readily can be seen how these multi-component apparatus can be relatively expensive.
The present invention is directed to a solution to these problems of complexity and cost by providing a very simple combination temperature responsive and pressure responsive apparatus wherein a single element is held in place within a pressure passage by a fusible bonding material and the element, itself, is designed to be pressure-rupturable.